Very recently, a special configuration of vertical MOSFETs was developed, these MOSFETs being referred to as TEDFETs (TEDFET=Trench Extended Drain Field Effect Transistor) and being distinguished by the fact that a drift control zone is provided adjoining the drift zone, said drift control zone being dielectrically insulated from the drift zone and being coupled to the drain zone of the component. In this case, a dielectric layer is arranged between the drift zone and the drift control zone and extends very deeply into the semiconductor material of the component according to the dimensions of the drift zone.
An electric field proceeding from the drift control zone is generated during operation of the TEDFET, and brings about an accumulation of charge carriers in the drift zone in an accumulation zone adjoining the dielectric layer.
In order to obtain a good effect-of the electric field proceeding from the drift control zone on the drift zone, it is advantageous to choose the dielectric layer to be precisely thin enough to provide the required insulation strength between drift zone and drift control zone.
In the vertical direction of the semiconductor body, the dielectric layer preferably extends down to depths approximately corresponding to the dimension of the drift zone in the vertical direction. Since the dielectric strength of a vertical component depends, inter alia, on the dimensions of the drift zone in the vertical direction, it may be necessary, particularly in the case of components having a high blocking capability, to provide large vertical dimensions for the drift zone—and accompanying this for the dielectric layer for the insulation of the drift zone. Approximately 5 μm to 15 μm, preferably approximately 10 μm extent of the space charge zone in the off-state case and thus of the drift zone and drift control zone are needed per 100 V required blocking capability of the component. All the vertical dimensions mentioned in the description below are oriented toward this relationship. By way of example, the required vertical dimension of the dielectric layer in the case of a TEDFET having a dielectric strength of 600 V may accordingly be between approximately 30 μm and 90 μm, preferably more than 50 μm.
In order to realize such components it is therefore necessary to produce dielectric layers between two semiconductor zones which, on the one hand, have to extend deeply into the semiconductor body in the vertical direction and on the other hand, are intended to have a small thickness. In this case, the ratio between the dimension of said dielectric layer in the vertical direction of the semiconductor body and its thickness, which is also referred to as the aspect ratio, may be more than 1000:1.
Such high aspect ratios in conjunction with a small thickness of the dielectric layer could not be realized heretofore.